Specifications for evolution of radio access methods and radio networks of cellular mobile communication (referred to as “Long Term Evolution (LTE)”, or “Evolved Universal Terrestrial Radio Access (EUTRA)” in the following) and are prepared in the 3rd Generation Partnership Project (3GPP). In LTE, Orthogonal Frequency Division Multiplexing (OFDM) method, which is multi-carrier transmission, is used as a communication method for radio communication from a base station apparatus to a mobile station apparatus (referred to as downlink; DL). Additionally, in LTE, Single-Carrier Frequency Division Multiple Access (SC-FDMA) method, which is single-carrier transmission, is used as a communication method for radio communication from a mobile station apparatus to a base station apparatus (referred to as uplink; UL). In LTE, Discrete Fourier Transform-Spread OFDM (DFT-Spread OFDM) method is used as SC-FDMA method.
In 3GPP, a radio access method and a radio network which realize much faster data communication using a wider frequency band than LTE (referred to as “Long Term Evolution-Advanced (LTE-A)” or “Advanced Evolved Universal Terrestrial Radio Access (A-EUTRA)” is under consideration. LTE-A is required to realize backward compatibility with LTE. It is required for LTE-A to allow an LTE-A-compatible base station apparatus to simultaneously communicate with both an LTE-A-compatible mobile station apparatus and an LTE-compatible mobile station apparatus, and for an LTE-A-compatible mobile station apparatus to communicate with an LTE-A-compatible base station apparatus and an LTE-compatible base station apparatus. In order to realize the requirement, in LTE-A, it is considered to support at least a channel structure which is identical to that of LTE. A channel implies a medium used for transmission of a signal, and there are, as types of channels, a Physical Downlink Shared CHannel (PDSCH) used for transmitting and receiving downlink data and control information, a Physical Downlink Control CHannel (PDCCH) used for transmitting and receiving downlink control information, a Physical Uplink Shared CHannel (PUSCH) used for transmitting and receiving uplink data and control information, a Physical Uplink Control CHannel (PUCCH) used for transmitting and receiving uplink control information, a Synchronization CHannel (SCH) used for establishing downlink synchronization, a Physical Random Access CHannel (PRACH) used for establishing uplink synchronization), and a Physical Broadcast CHannel (PBCH) used for transmitting downlink system information. The mobile station apparatus or the base station apparatus allocates, onto respective channels, signals generated from control information, data or the like, and transmits them.
The control information allocated to the physical uplink control channel is referred to as an Uplink Control Information (UCI). The uplink control information includes control information (ACK/NACK) indicating Acknowledgement (ACK) or Negative Acknowledgement (NACK) for the data allocated in the received physical downlink shared channel, control information (Scheduling Request: SR) indicating an assignment request of an uplink resource, or control information (Channel Quality Indicator: CQI) indicating downlink reception quality (also referred to as channel quality).
In LTE-A, a technique (also referred to as Spectrum aggregation, Carrier aggregation, Frequency aggregation, etc.) which uses a plurality of frequency bands having a channel structure which is identical to that of LTE (referred to as “Component Carrier: CC” in the following. Also referred to as element frequency band.) as a single frequency band (wide frequency band) is under consideration. Specifically, in communication using Carrier aggregation, a downlink channel is transmitted and received for each downlink CC (referred to as downlink component carrier; DL CC in the following), and an uplink channel is transmitted and received for each uplink CC (referred to as uplink component carrier; UL CC in the following). In other words, Carrier aggregation is a technique by which a base station apparatus and a mobile station apparatus transmit and receive signals simultaneously via a plurality of channels using a plurality of component carriers in downlink and uplink.
In LTE-A, a configuration in which the base station apparatus performs communication using an arbitrary frequency band is referred to as a “Cell”. Carrier aggregation is communication via a plurality of cells using a plurality of frequency bands, which is also referred to as Cell aggregation. In Cell aggregation, a plurality of cells is defined as two different types of cells, with one cell defined as a Primary Cell (Pcell) and the other cell defined as a Secondary Cell (Scell). The base station apparatus performs setting of a primary cell and a secondary cell independently for each mobile station apparatus using Cell aggregation. A primary cell necessarily includes a set of one downlink component carrier and one uplink component carrier. A secondary cell includes at least one downlink component carrier, and may or may not include an uplink component carrier. A component carrier used in a primary cell is referred to as a Primary Component Carrier (Primary CC, PCC). A component carrier used in a secondary cell is referred to as a Secondary Component Carrier (Secondary CC, SCC). In a primary cell and a secondary cell, although data communication using a physical downlink shared channel and a physical uplink shared channel is performed in common, various other processes are performed in a different manner. To be brief, a plurality of processes is performed only in a primary cell but not performed in a secondary cell. For example, in a primary cell, acquisition of system information and determination of insufficient radio quality (RLF: Radio Link Failure) are performed in the downlink, whereas execution of random access procedure using a physical random access channel, transmission and reception of uplink control information using a physical uplink control channel, or the like are performed in the uplink. Basically, all the processes performed in LTE which does not use Cell aggregation are performed in a primary cell, whereas a plurality of processes other than data communication is not performed in a secondary cell.
A mobile station apparatus uses a physical uplink control channel to transmit a reception confirmation response (ACK/NACK) indicating Acknowledgement or Negative Acknowledgement for data received using a physical downlink shared channel. The base station apparatus performs retransmission control of a physical downlink shared channel, based on the reception confirmation response received from the mobile station apparatus. With LTE-A using Cell aggregation, the base station apparatus can simultaneously use a plurality of physical downlink shared channels to transmit data to a mobile station apparatus. A mobile station apparatus which receives a plurality of physical downlink shared channels using Cell aggregation must simultaneously notify a plurality of reception confirmation responses to the base station apparatus, using a resource for a physical uplink control channel of a primary cell. In LTE, the base station apparatus can only use a single physical downlink shared channel at a time to transmit data to a mobile station apparatus, and the mobile station apparatus which received a single physical downlink shared channel uses a physical uplink control channel to notify the base station apparatus of a single reception confirmation response. With LTE-A, introduction of a physical uplink control channel with a new transmission method and signal configuration is under consideration in order to allow a mobile station apparatus to transmit a plurality of reception confirmation responses to the base station apparatus (Non-patent document 1). Anew transmission method (ACK/NACK channel selection) is under consideration, which uses a plurality of physical uplink control channels to implicitly indicate information of the reception confirmation response by selecting a physical uplink control channel to be used for signal transmission according to information of a plurality of reception confirmation responses, and also to explicitly indicate the information of reception confirmation response by transmitting a signal modulated in the selected physical uplink control channel. A physical uplink control channel using DFT-Spread-OFDM method is under consideration as a new signal configuration.
In LTE, assignment of a resource of a physical uplink control channel used for transmitting a reception confirmation response is implicitly performed based on a resource used for a physical downlink control channel. Implicit resource assignment means that information just for assigning a resource is not used but resource assignment is performed diverting other information. On the other hand, explicit resource assignment means that information just for assigning a resource is used and resource assignment is performed. A physical downlink control channel includes a plurality of Control Channel Elements (CCEs). Resources of the physical uplink control channel used for transmitting a reception confirmation response are preliminarily associated with the control channel elements, which are resources used for the physical downlink control channel. A CCE used between the base station apparatus and the mobile station apparatus is provided with a number for identifying the CCE. Numbering of a CCE is performed based on a preliminarily defined rule.
A physical downlink control channel includes a set of a plurality of CCEs (CCE Aggregation). The number of CCEs constituting the set is referred to as a “CCE aggregation number” in the following. A CCE aggregation number constituting a physical downlink control channel is set in the base station apparatus according to the coding rate set for the physical downlink control channel and the number of bits of the control information included in the physical downlink control channel. For example, the base station apparatus forms a physical downlink control channel by one CCE, two CCEs, four CCEs, eight CCEs, and so on. For example, the base station apparatus uses a physical downlink control channel having a small number of CCEs for a mobile station apparatus with a good channel quality, and uses a physical downlink control channel with a large number of CCEs for a mobile station apparatus with a poor channel quality. Additionally, for example, the base station apparatus uses a physical downlink control channel with a small number of CCEs when transmitting control information with a small number of bits, and uses a physical downlink control channel with a large number of CCEs when transmitting control information with a large number of bits.
A physical uplink control channel used for transmitting a reception confirmation response includes three-dimensional resources, namely, physical resource blocks, frequency domain codes, and time domain codes. For a combination of respective resources of a physical uplink control channel used for transmitting a reception confirmation response used in a communication system, a number for identifying the combination of respective resources is provided based on a preliminarily defined rule.
A CCE number and a resource number of a physical uplink control channel used for transmitting a reception confirmation response is preliminarily associated with each other, so that a CCE is associated with a resource of the physical uplink control channel both having a same number. A mobile station apparatus uses a resource of a physical uplink control channel having a number corresponding to a CCE having the smallest number among the CCEs used for the physical downlink control channel which has detected control information addressed to its own apparatus, and transmits a reception confirmation response to data of the physical downlink shared channel for which resource assignment is indicated by the physical downlink control channel. The base station apparatus, similarly recognizing the correspondence between the CCE number and the resource number of the physical uplink control channel used for transmitting a reception confirmation response as with the mobile station apparatus, assigns a CCE to be used in the physical downlink control channel, considering the resource of the physical uplink control channel to be assigned to the mobile station apparatus. In other words, the mobile station apparatus recognizes the resource of a physical uplink control channel used for transmitting a reception confirmation response assigned to its own apparatus, based on the CCE used for the physical downlink control channel which has detected the control information addressed to its own apparatus.
For LTE-A using Cell aggregation, a method of assigning a resource of a physical uplink control channel with a new transmission method and the signal configuration is under consideration, with regard to a reception confirmation response (Non-patent document 2). First, assignment of a resource of the physical uplink control channel when transmitting a reception confirmation response using ACK/NACK channel selection will be described. When transmitting a physical downlink control channel via a primary cell, a resource of the physical uplink control channel associated with the CCE of the physical downlink control channel is implicitly assigned to the mobile station apparatus, as with LTE. When transmitting a physical downlink control channel via a primary cell, the physical downlink shared channel having resource assignment information included in its physical downlink control channel is transmitted via a primary cell or a secondary cell. When transmitting a physical downlink control channel via a secondary cell, a resource of the physical uplink control channel is explicitly assigned to the mobile station apparatus using predetermined signaling, unlike LTE. As the predetermined signaling, a method of explicitly assigning a resource of the physical uplink control channel using RRC (Radio Resource Control) signaling, and a method of explicitly assigning a resource of the physical uplink control channel using control information of the physical downlink control channel are under consideration. With the method of explicitly assigning a resource of the physical uplink control channel using RRC signaling, a resource of the physical uplink control channel has been preliminarily assigned for the mobile station apparatus before starting data communication using Cell aggregation, and the mobile station apparatus, upon detecting a physical downlink control channel in a secondary cell, in other words, upon recognizing that a physical downlink control channel has been transmitted via a secondary cell, uses a resource of the physical uplink control channel preliminarily assigned by RRC signaling as resources to be used for selection of a physical uplink control channel performed in order to implicitly indicate the information. With the method of explicitly assigning a resource of the physical uplink control channel using control information of the physical downlink control channel, the mobile station apparatus, upon detecting a physical downlink control channel in a secondary cell, uses the resource of the physical uplink control channel indicated in the control information of the detected physical downlink control channel as resources to be used for selection of a physical uplink control channel in order to implicitly indicate the reception confirmation response information. With the method of explicitly assigning a resource of the physical uplink control channel by the control information of the physical downlink control channel, candidates of a plurality of resources of the physical uplink control channel have been preliminarily assigned to the mobile station apparatus by RRC signaling, and one of the candidates of the resources which has been set by RRC signaling using control information of the physical downlink control channel is presented.
As the control information indicating resources of the physical uplink control channel in the physical downlink control channel, control information which is usually used for other purposes may be diverted. Here, diverting control information means that a control information field for a first case is interpreted as first control information and that for a second case is interpreted as second control information, with the first case being different from the second case and the first control information being different from the second control information. For example, the control information field, which is interpreted as control information indicating a transmit power control value of the physical uplink control channel when transmitting the physical downlink control channel via a primary cell, may be interpreted as the control information indicating resources to be used in selection of a physical uplink control channel performed in order to implicitly indicate the reception confirmation response information when transmitting the physical downlink control channel via a secondary cell.
Next, assignment of a resource of the physical uplink control channel using DFT-Spread-OFDM method will be described. When a physical downlink shared channel is transmitted at least via a secondary cell, resources of the physical uplink control channel are explicitly assigned to the mobile station apparatus, using predetermined signaling, unlike LTE. As the predetermined signaling, a method of explicitly assigning a resource of the physical uplink control channel using control information of the physical downlink control channel is under consideration, as with the case of transmitting a reception confirmation response using ACK/NACK channel selection. When transmitting a physical downlink shared channel only via a primary cell, a method of implicitly assigning a resource of the physical uplink control channel associated with the CCE of the physical downlink control channel to the mobile station apparatus, as with LTE, and a method of explicitly assigning a resource of the physical uplink control channel to the mobile station apparatus using predetermined signaling, unlike LTE, are under consideration. When the method of implicitly assigning, to the mobile station apparatus, resources of the physical uplink control channel associated with the CCE of the physical downlink control channel in a case where a physical downlink shared channel is transmitted only via a primary cell, the signal configuration of the physical uplink control channel is not one that uses DFT-Spread-OFDM method but uses a physical uplink control channel with a signal configuration similar to that of LTE. A physical downlink control channel including resource assignment information of the physical downlink shared channel to be transmitted via a primary cell is transmitted only via a primary cell, whereas a physical downlink control channel including resource assignment information of the physical downlink shared channel to be transmitted via a secondary cell is transmitted via a primary cell or a secondary cell.
Additionally, in LTE-A, it is considered that a mobile station apparatus transmits signals by using a plurality of transmitting antennas to realize faster data communication than LTE or improve the signal error quality over the uplink. In LTE-A, it is considered to apply diversity transmission (also referred to as transmission diversity) using a plurality of transmitting antennas for the physical uplink control channel (Non-patent document 3). For example, as methods of diversity transmission to be used by a mobile station apparatus, there are methods under consideration such as a method modulating uplink control information by the mobile station apparatus, generating a plurality of signals obtained by multiplying different orthogonal codes to the modulated signal, and transmitting the signals obtained by multiplying the orthogonal codes respectively via different transmitting antennas; a method generating a plurality of signals obtained by multiplying a code sequence with a cyclic shift of different values applied to the modulated signal and transmitting the signals obtained by multiplying the code sequence respectively via different transmitting antennas; or a method generating a plurality of modulated signals and transmitting the signals allocated over different time/frequency resources via respectively different transmitting antennas. As a method of assigning a resource used for transmission diversity to a physical uplink control channel, which has neither a transmission method using a physical uplink control channel to be used for transmitting a reception confirmation response in LTE, in other words, using ACK/NACK channel selection in LTE-A, nor a signal configuration using a DFT-Spread-OFDM method, a method is considered in which a resource of the physical uplink control channel corresponding to the CCE having the smallest number among one or more CCEs constituting the physical downlink control channel is assigned for a first transmitting antenna, and a resource having the next number to the resource of the physical uplink control channel is assigned for a second transmitting antenna (Non-patent document 4). In other words, according to the method described above, a resource having the next number to the resource of the physical uplink control channel assigned to the first transmitting antenna is assigned for the second transmitting antenna.